Effect of hot isostatic pressing on microstructure and mechanical properties of CM-681LC nickel-base superalloy using microcast

Abstract

This study investigates how hot isostatic pressing (HIP) affects the microstructure and fracture modes of CM-681LC superalloy. As-cast test bars with grain size of 80 μm were prepared using the fine-grain process followed by HIP. Experimental results indicate that micropores formed during solidification and contraction degrade the tensile strengths and elongations of the fine-grain CM-681LC superalloy before HIP. The area fraction of micropores was reduced from 0.2% to 0.06% following HIP. Scriptlike MC carbides decompose into particlelike M23C6 carbides during HIP, revealing that HIP refines and spheroidizes the carbides. Eliminating the micropores and refining the carbides increases the mechanical strength by up to about 9% and the elongation by over 10% in room- and high-temperature tensile tests. The fracture analyses after tensile tests of the fine-grain test bars reveal that the microporosity and the scriptlike carbides at the grain boundaries are the main causes of the fracture of the test bars before HIP. The fracture mode of the fine-grain test bars following HIP, according to the tensile test, is typically intergranular because the micropores are eliminated and the carbides are refined. Since the elimination of the micropores and refinement of the carbides by HIP effectively improves the tensile strength and elongation, the fine-grain casting yields favorable mechanical properties. © 2008 The Japan Institute of Metals.